1. Field of the Invention
The present invention relates to a method of testing a magnetic disc device, and, more particularly, it relates to a method of testing a magnetic disc device to detect a deviation of a track attributable to an abnormal track pitch.
2. Description of the Related Art
In general, a magnetic disc device uses a write head to record data or information into a magnetic disc, and uses a read head to reproduce the recorded data or information. In recent years, most magnetic disc devices have a write head and a read head combined with each other, instead of using one head to read and write data. When the write head writes data on a disc, the read head is used to read positioning information or servo information, which is written in advance in a magnetic disc as a servo pattern, so as to position the write head on a predetermined track. When the read head reads, the read head is positioned on a predetermined track so as to read the data, based on the servo information read by the read head.
Therefore, a servo pattern needs to be written at a constant feeding pitch or a constant track pitch so as to correctly indicate a track position. However, at the time of writing a servo pattern into a disc, a track can have an uneven track pitch in some cases. This track-pitch deviation occurs when a voice coil motor that moves the write head to write the servo pattern does not rotate satisfactorily, or when a push pin that moves the head to be used by a servo track writer is contacted unsatisfactorily, or when an environmental shock occurs. This track-pitch deviation similarly occurs at the time of writing a servo pattern on a magnetic disc after the magnetic disc is assembled into a magnetic disc device, or at the time of writing a servo pattern on a magnetic disc before the magnetic disc is assembled into a magnetic disc device.
A track of which the track width has become too small cannot be used. When a read head and a write head are provided separately, a relationship between the read head and the write head changes due to a deflection angle of an arm on which the head is mounted, and the relationship between the read head and the write head also changes due to a deviation of a track width. In other words, when there are narrow or wide tracks between the read head and the write head, it is not possible to accurately control the write head position on a predetermined track based on the read head position.
Correction of a deviation that occurs due to a deflection angle or a yaw angle of the arm is known as described in Japanese Patent Application Unexamined Publication No. 2000-322848. However, the technique described in this publication is not designed to detect a deviation of a track caused by an abnormal track pitch.